1. Field of the Invention
The present invention relates to gas regulator valves and apparatus for measuring the quantity of gas, notably hydrocarbons, leaving a tank or other pressurised container.
2. Description of the Related Art
Using a meter mounted directly on a tank does indeed enable the tank to be delivered with its meter already fitted at the factory, but this has the following drawback. The meter, which is often a membrane-type meter, measures volumes of gas, irrespective of the density of the gas. Under certain conditions, e.g. a fast flow rate, a very low external temperature, tanks buried in the ground, the temperature of the gas may drop considerably and the density of the product may increase accordingly. The distribution company then supplies more gas than the meter indicates.
German patent no. 721 896 remedies this by mounting, upstream or downstream of a volumetric meter, a valve displaced by a membrane subjected to the opposed forces of the pressure of the gas and the pressure of an auxiliary fluid coming from a reservoir which takes the temperature of the gas. This throttle valve for the gas has a pressure-reducing effect, but it alters the flow rate of the gas. For reasons of work organisation it is undesirable for the flow rate and hence the time taken to fill a tank to be dependent on the temperature, more especially as any variation in this length of time would otherwise be an indication of a fault.
The invention remedies this disadvantage with a gas regulator valve comprising means for lowering the pressure of a gas current to a specified pressure while maintaining the flow rate.
According to the invention, the relief pressure in the regulator valve is varied as a function of either the temperature of the gas or the ambient temperature. In this way, the last stage of pressure relief situated just in front of the meter is controlled around its nominal specified level by a device controlled by the temperature of the gas and arranged so that the pressure variation compensates for the variations in density caused by the variations in temperature. Thus, when the gas is very cold and therefore very dense, the relief pressure is lowered so as to compensate for the increase in density. Conversely, when the temperature rises, the relief pressure of the final stage of pressure relief, located just upstream of the meter, is increased.
The invention also relates to a measuring device mounted, in particular, on a tank comprising a gas regulator valve according to the invention upstream of a meter adapted to measure the volume of gas passing therethrough. Preferably, the gas regulator valve comprises a body subdivided by a membrane into a first compartment in which a spring applies a force to the membrane and a second compartment into which an inlet tube and an outlet tube open and in which is mounted a regulating mechanism, comprising a valve and seat, operating as a function of the position of the membrane subjected to the pressure of the gas prevailing in the second compartment. The means intended to modify the specified pressure comprise a bellows in contact with the spring and supplied with a readily expandable fluid or a liquefied gas which may be of the same type as the gas which is to be measured, coming from a capsule placed in the inlet tube or outside the regulator valve and exposed to ambient temperature.